Method for identifying optimal regions for cardioversion therapy (variants)

ABSTRACT

The group of inventions relates to medicine (physiotherapy). Electric stimuli which are generated by the following ringing circuit: active electrode-inductive storage unit-passive electrode-interelectrode tissues-active electrode, contain oscillations which are used as a test signal. In one variant of the method the electrodes are successively applied (in another variant—moved uniformly) across the skin area. Every time the electrodes-to-skin contact is detected, the oscillation parameters are recorded after a delay. Moreover, the values of parameters can be averaged. The group of invention provides the use of both combined and disjointed (separated) electrodes. An optimal zone for electropulse therapy is identified by minimal or maximal value of one or more parameters of the aforementioned oscillations and the use of the principle of “small asymmetry”. The group of inventions provides an increase in the accuracy with which zones optimal for electropulse therapy are identified and localized.

CROSS REFERENCE TO RELATED APPLICATIONS

The present patent application is a National stage patent applicationfrom PCT application PCT/RU2017/000080 filed Feb. 17, 2018 which claimspriority to Russian patent application RU2016107880 filed Mar. 3, 2016.

TECHNICAL FIELD

The group of inventions refers to physiotherapy, in particular, themeans of electropulse stimulation of the human skin by SCENAR devicesand similar to those, in which the inductive energy storage unit is usedfor generating stimuli, and can be used in diagnostic, therapeutic,rehabilitation and preventive purposes.

BACKGROUND OF THE INVENTION

Currently, the stimulators using this principle are manufactured inRussia (SCENAR, DENAS, TINER, etc.) as well as in other countries(Interx, Avazzia, Physiokey, etc.).

An important aspect of the use of such stimulators is the search for thezones optimal for electric stimulation.

The use of inductive energy storage unit for stimuli generation allowsto assess the reaction of the inter-electrode tissues (primarily skin)along with the stimulation, to evaluate the body's reaction to thestimulation in general, and thus, to evaluate the electrophysiologicalcondition of a body.

From the summary and the description of the device in RU Patent No.2068277, IPC 6 A61N1/36, published on 27 Oct. 1996, results a method,according to which the active and passive electrodes, connected to aswitch amplifier with an output transformer, are placed on the patient'sskin, the parameters of free oscillations that arise during that aremeasured, and body reaction to the stimulation is identified by thespeed of changing of duration of the first half wave of theaforementioned oscillations, whereas the nature of pathology isidentified by duration of the first half wave of these oscillations.(Free oscillations are mistakenly called forced oscillations in thedescription).

This method allows the evaluation of the body's reaction to thestimulation with the selected criteria, but does not provide for thesearch of zones optimal for electropulse therapy, which can be carriedout using the same criteria by identifying the skin areas that are mostdifferent from those of the surrounding skin.

The drawback of this method is the considerable dependence of theparameters of free oscillations on the speed and force of the electrodepressing to the patient's skin, especially when the electrodes are beingapplied to the skin.

Their minor deviations may result in significant differences in themeasured values of free oscillations parameters and, therefore, anincorrect identification of the body's reaction to the stimulation orthe nature of pathology.

Another drawback of this method is the lack of averaging of measuredvalues, which can also lead to a significant error in the evaluation ofthe body's reaction to the stimulation or the nature of pathology due tothe high variability (dynamic properties) of the signal.

In addition, this method does not provide an evaluation of the body'sreactions to the stimulation when the electrodes are moved along theskin.

The closest to the proposed one method of evaluating theelectrophysiological condition of the human body is to apply electrodesto the skin, transmit an electric signal from high-quality inductor coilsaturated with electromagnetic power through the interelectrode tissue,and use as a test signal the electric oscillations arising in theringing circuit, formed by the following parts: active electrode-ahigh-quality inductor coil-passive electrode-interelectrodetissue-active electrode, an evaluation of the electrophysiologicalcondition of the body by measuring the frequency, or amplitude, ordamping of these oscillations (RU Patent No. 2161904 C2, A61V5/05, A61N39/00, published on 20 Jan. 2001).

This method allows to perform the evaluation of the electrophysiologicalcondition of the human body or, according to the description of theinvention, of its particular organs and systems, using the results ofmeasuring the parameters of free oscillations arising during the saidstimulation.

Although this method does not support the searching of the optimal zonesfor electropulse therapy, it can also be used for these purposes byidentifying the skin areas that are most different from the surroundingones by the measurements of frequency, or amplitude, or damping ofoscillations occurring in the aforementioned ringing circuit.

However, due to the lack of delay between the application of electrodesto the skin and the measurement of oscillations parameters, and alsobecause there is no averaging of oscillation parameter values, thismethod cannot ensure the gage reproducibility in case of deviations inthe speed of electrode application or the force of electrode pressing tothe patient's skin.

Another drawback of this method is that it allows an evaluation of theelectrophysiological state only in static condition, and does not allowit to be carried out when the electrodes are moved along the skin.

SUMMARY

The aim to which the proposed invention is directed is to minimize theinfluence of such unavoidable subjective factors as non-uniformity ofthe speed of application and force of pressing of the electrodes on theskin on the results of measurement of parameters of free oscillations,which appear during the electropulse stimulation with stimuli generatedby the inductive energy storage unit when searching for optimal zonesfor electropulse therapy by successive electrode applications.

As a result, the reliability of identification and accuracy oflocalization of optimal zones for electropulse therapy are increasedwhen parameters of free oscillations are used for their searching.

The second aim to which the proposed invention is directed is to providethe possibility of searching optimal zones for the electropulse therapyduring the labile method of stimulation, when the electrodes are moveduniformly across the entire surface of the chosen skin area.

The technical result of using the proposed method is the increasing ofobjectivity and accuracy in identifying the optimal zones forelectropulse therapy by reducing the influence of subjective factors,and, also, providing the possibility of such search during labilestimulation.

By the optimal zone for electropulse therapy is understood the zone onthe surface of chosen skin area, which is most different from otherparts of the same surface.

Several contiguous zones are considered one zone.

If several non-contiguous zones with equal parameters are found, thezone with the smallest of them is considered as the optimal zone forstimulation.

The technical result of the invention is:

during the electrostimulation, which includes applying electrodes on theskin and transmitting electric pulses through the electrodes frominductive energy storage unit, the device's electrodes are successivelyplaced across the entire surface of the chosen skin area and, after aset period between 0.1-0.5 sec following each detection of contactbetween the electrodes and the skin, the oscillation parameters areaveraged and recorded, whereas the optimal zone for electropulse therapyis identified by minimum or maximum averaged value of one of theoscillation parameters or by the averaged oscillation parametersachieving the predefined criterion.

If several non-contiguous zones with equal averaged extreme parametervalues or equal criterion values are found, the smallest of them isconsidered as the optimal zone for stimulation.

The second variant, instead of successive placing, is the labile(movable) stimulation by electrodes of the chosen skin area. In thiscase, the electrodes are moved uniformly across the entire surface ofthe area in one or more repetitions, and, after a set period of between0.1-0.5 seconds following each detection of contact between theelectrodes and the skin, the minimums and maximums of one of the freeoscillation parameters, or the consistency of the values of theoscillation parameters with the predefined criterion are found andrecorded, and the optimal zone for the electropulse therapy isdetermined by the minimum or maximum value of one of the oscillationparameters, or by achievement of the predefined criterion by theparameter values.

In this method, extremes or criteria can also be found for averagedparameter values.

If in any of these subvariants several non-contiguous zones with equalaveraged extreme parameter values (instantaneous or averaged,respectively) or equal criterion values are found, the smallest of themis considered as the optimal zone for stimulation.

Both variants provide for the use of the combined electrode, containingboth active and passive electrodes, and disjointed (separated, splitted)ones, where the active and passive electrodes are constructivelyseparated, with one of them placed outside the chosen skin area and thesecond one applied or moved within it.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained by the following drawings:

FIG. 1 is a functional diagram of the output stage of SCENAR device andthe electrical equivalent of interelectrode tissues of the biologicalobject;

FIG. 2 illustrates the change of the capacity and active resistance ofthe double-layer over time;

FIG. 3 illustrates an example of a stimulus shape.

FIG. 4 illustrates the stimuli shape before the electrodes are appliedto the skin;

FIG. 5 illustrates the stimuli shape right after the electrodes areapplied to the skin;

FIG. 6 illustrates the stimuli shape 5 seconds after the application ofthe electrodes to the skin;

FIG. 7 illustrates the stimuli shape 30 seconds after the application ofthe electrodes to the skin.

DETAILED DESCRIPTION OF THE INVENTION

The first variant is to search the optimal zones for electropulsetherapy by the successive placement of the electrodes.

It is known that when the electrodes contact the skin surface, which isgenerally a complex mixture of aqueous solutions, a number of processesoccur at the “metal-solution” boundary.

This is, above all, the formation of the difference of potentials(double electric layer) called electrode potential (Grechin, V. (1997),“Neurophysiology techniques,” Nauka, p. 7-9).

The functional diagram of the output stage of the device, thatinfluences by the stimuli generated with the inductive storage unit, isshown in the FIG. 1.

The output stage includes inductive energy storage unit 1 with internalactive resistance 2, connected to the power source 3 through switch 4and to electrodes 5 and 6, which are placed on the tissue of thebiological object, the electric equivalent of which is presented by theRC circuit 7 (see Popechitelev, E. P. and M. Kornevski, (2002),“Electricophysiological and photometric medical equipment. Theory andDesign,” Vysshaya Shkola, p. 64-65). This circuit includes the Rpresistance, the double-layer capacity C and the interelectrode tissues'resistance rs.

The interelectrode impedance for impulse current is almost entirelydetermined by the impedance of the double electric layer Rp and C, whichchanges over time during the formation of the aforementioned layer, bothcomponents are changed significantly and also quite quickly immediatelyafter the electrodes are placed on the skin.

General change of Rp and C over time is shown on FIG. 2 (Popechitelev,E. P. and M. Kornevski, (2002), “Electricophysiological and photometricmedical equipment. Theory and Design,” Vysshaya Shkola, p. 72).

On FIG. 2 the time of formation of the double-layer capacity is markedas t1.

After that, the changes of the double electric layer's impedance (Rp andC) are negligible and determined primarily by the electro-chemicalreactions associated with the local metabolism under the electrodes.

The influencing stimuli are generated in the following way.

In the initial position, switch 4 is open.

When switch 4 is closed, the first stage of the stimulus generationbegins, in which the voltage from power supply 3 is applied to theinductive storage 1, which causes a flow of a linearly increasingcurrent through it, and, thus, the accumulation of electromagneticenergy by inductive storage 1.

That is, the energy is “pumping” into inductive storage 1, and, hence,the other name of the first stage of the stimulus is “pumping”.

At this stage, the inductive storage 1 with active resistance 2, as wellas the power source 3 with the switch 4 are connected parallel tointerelectrode tissues 7.

As the internal resistance of the power supply 3 and switch 4 (aroundseveral Ohm, these resistances are not shown on the diagram due to thesmall values) are significantly less than impedance of interelectrodetissues 7, the stimulus shape during the first stage is almostindependent from the impedance of interelectrode tissues 7.

After the specified amount of power is reached, inductive storage 1 isdisconnected from power source 3, breaking switch 4.

The second stage of the stimulus generation begins, in the process ofwhich the energy accumulated during the previous stage by inductivestorage 1, is transferred through electrodes 5 and 6 to the tissues ofbiological object 7 and generates free electric oscillations in theringing circuit, formed by the inductivity of the storage 1 and theimpedance of interelectrode tissues 7.

Now the small inner resistance 2 of the inductive storage 1 is connectedsequentially with impedance of interelectrode tissues 7, so the shape ofthe oscillations is completely determined by the impedance ofinterelectrode tissues 7 and the induction of the storage 1.

The other name of the second stage is “free oscillations”.

This method of creating of oscillations is known as “shock excitation”,and the mentioned circuit is known as the shock-excited oscillatorycircuit or the ringing circuit.

An example of the shape of a two-stage stimulus generated with inductivestorage unit is presented in FIG. 3.

To illustrate how changes of Rp and C affect the type of freeoscillations, FIG. 4-7 shows stimuli oscillograms before the electrodesare applied to the skin, immediately after application, and 5 and 30seconds after application, obtained when using the SCENAR device(Technical Conditions/TC 9444-015-05010925-2004.).

From the presented oscillograms and graphs of changes of Rp and C overtime it is clear that the parameters of free oscillations immediatelyafter the electrodes are placed on the skin changes significantly, andthe changes depend, also, on speed of placing of electrodes on the skin,on degree and uniformity of their pressure.

Introduction of a certain constant delay between the primary contact ofelectrodes and skin and the beginning of measurement of freeoscillations which result will be used later to search for special zonesallows to level the said factors to a large extent.

The delay duration must be sufficient to establish a firm contactbetween the electrodes and the skin, but not too large to provide formeasurement on the initial area of graphs on FIG. 2, i.e. significantlybefore the t1 time expires.

Since this time is a few seconds, and the placing of the electrode onthe skin from the first contact to dense pressing makes no more than0.1-0.2 sec, it is reasonable to set the specified delay within 0.1-0.5sec.

The averaging of the measured values allows to additionally reducedependence on the subjective factors of the electrode placing.

As the measurements are not conducted continuously but at the rate ofstimuli generation, then the minimum averaging time is the double periodof the stimuli sequence (for paired averaging), and the maximum oneshould not exceed the time of formation of the t1 double layer.

Thus, the averaging time should be within a range between severalhundredths of a second and one or even two seconds. Averaged values canbe presented to a doctor for later comparison or can be saved in thedevice's memory.

In a homogeneous section of the body (back, stomach, shoulder, forearm,neck-collar zone etc.), the optimal zones for electropulse therapy areidentified by extreme deviation of one of the parameters of freeoscillation from the other electrode placing or by achievement of acertain criterion on their basis.

Thus, an area of skin with maximum (minimum) averaged duration of thefirst free oscillation (or its first half-wave, as described in RUPatent No. 2068277), or with maximum (minimum) averaged duration of oneof the subsequent free oscillations, or with maximum (minimum) averagednumber of free oscillations, or with maximum (minimum) change rate ofthe duration of the first free oscillation (or one of the subsequentoscillation) can be considered the optimal zone for electropulsetherapy.

The skin area where the combination of measured parameters is reachedcan also be considered as the optimal zone for electropulse therapy.

More complex methods of zone identifying can be used on the basis of apredefined criterion—some predefined combination of values of measured(or averaged) oscillation parameters or the value of the oscillationparameter under certain condition.

For example, the criterion for selecting the optimal zone may be themaximum duration of the first free oscillation, with a minimum number ofoscillations, or the maximum duration of the first free oscillationafter the dynamics (change) of the oscillation has ceased.

As the proposed method for selecting optimal zones for the electropulsetherapy uses extreme values of one of the free oscillations parameters,or reaching a certain criterion based on one or more oscillationparameters, then it is sufficient to indicate the moments of reachingthe new extreme or the criterion rather than showing their values to adoctor.

In the simplest case, a doctor must memorize localization of only thelast place where the extremes were reached, and it will be the optimalzone for the electropulse therapy.

If several zones with equal extreme parameter values are found, then inorder to improve the efficiency of the therapy it is reasonable to treatnot all of them, but only the so-called “small asymmetry” zones—theareas of skin surface which differ from the surrounding surface andwhich are small in relation to the entire surface treated (Gorfinkel, Y.(1996),

“Theoretical and practical basis for improving the effectiveness ofSCENAR therapy,” SCENAR therapy and SCENAR Expertise collection 2: p.16-18). The considered method of improving the effectiveness of therapyprovides for the stimulation of only one of the found areas with equalextreme parameter values (or criterion), which is the smallest.

In the SCENAR therapy the labile stimulation is also applied, whichfacilitates the subjective determination of optimal zones forstimulation.

Therefore, the second variant is to search for special zones with theelectrodes moved uniformly across the entire surface of the chosen skinarea in one or more repetitions.

When the electrodes are moved on the skin, the same processes ofdouble-layer formation occur, with the difference that new skin areastake part in the formation of the layer, while the treated ones areleaving the interelectrode space.

Thereby, the double-layer formation is not complete and the double-layerstate is described as part of the graph on FIG. 2, located substantiallyto the left of the time t1.

In this case, the introduction of a constant delay between the electrodecontact with the skin and the start of the measurement of freeoscillations parameters will also allow to reduce the dependence ofmeasured values on the subjective peculiarities of placing theelectrodes on the skin.

After being firmly pressed on the skin the electrodes are moved withinthe selected zone.

When the size of the zone is significantly big (abdomen, back) then itis impossible to move the electrodes evenly on the entire surface withone movement.

The treatment of the zone with several movements of electrodes may alsobe provided for by methodological techniques.

In that case the surface is being treated with several movements in onedirection (for example, from top to bottom) taking the electrodes offthe skin and placing them back to the beginning of a new movement.

Introduction of a constant delay between the determination of thecontact with the skin and the beginning of measurement of oscillationsparameters when stimulating the zone in one or more repetitions allowsto eliminate the error caused by non-uniformity of every placement ofthe electrodes on the skin.

The measurements can be conducted at the stimuli rate, whereas theindication, as in the first variant, can be only made when the newextreme or criterion is reached.

To reduce the error caused by the uneven movement of electrodes,resulting in uneven change of impedance of Rp, C and, consequently,uneven change of the parameters of free oscillations, it is useful toaverage the results of measurements.

The averaging can be carried out either with the several sequentialmeasurements (simple averaging) or with a “sliding window” (movingaveraging).

The labile method also applies the principle of “small asymmetry”, i.e.the impact on that identified zone with equal extreme parameter values,which is the smallest.

Both variants provide for the use of the combined electrode, containingboth active and passive electrodes, as well as disjointed (separated)electrodes, where the active and passive electrodes are constructivelyseparated. One of them is placed outside the zone selected fortreatment, and the other is successively placed or moved within it.

The proposed method is performed as follows.

The electrodes are applied to the skin in the area close to thetreatment zone, but outside of it.

The level of electrostimulation is set, for example, according toindividual sensations, usually at a comfortable level.

The other electrostimulation parameters are also set manually orautomatically in accordance with the selected therapy technique.

The method of searching optimal zones for electropulse therapy ischosen—sequential or labile.

During sequential method of treatment the electrodes are placed on theskin, and, 0.1 to 0.5 sec after the detection of contact with skin (bymeasuring the parameters of free oscillations caused by formation ofdual-layer capacity, or by measuring the current flowing through theelectrodes), the parameters of free oscillations are measured andaveraged during a set period, for example, 1 second.

The stimulation is then stopped, and, in the simplest case, the doctoris provided with result of the measurement of oscillations parameters orthe calculated value of the criterion.

The electrodes are then taken off the skin (the device is removed fromthe skin) and placed to the next point.

By comparing the received values (numerical or mnemonic, for example,the brightness of the glowing LED, or the number of LEDs glowing, orpitch of the sound tone, or the clicking sound rate), the doctoridentifies the zones optimal for electropulse therapy.

In order to eliminate redundant information during the next successiveplacings of the electrodes, only the information about the achievementof a new extreme (or criterion) can be provided, whereas it is enough toindicate the end of the averaging time if no new extremes (or criterion)have been achieved at the new placing point.

The device itself can record the extreme zones by identifying them, forinstance, with the sequential index of the electrode placing.

It is also possible to make a video recording of the electrodesapplication points and to link the measured values to them.

When computer is used for these purposes, the identification of zonesoptimal for electropulse therapy and their localization can be fullyautomated.

According to the results of the optimal zone identification, aftersearching through the entire chosen skin area, the main therapy iscarried out, according to the chosen technique.

If several non-contiguous zones were found, then the smallest zone isconsidered optimal for electropulse therapy.

During the labile method of searching, after setting the individuallevel and parameters of electrostimulation as described above, theelectrodes are placed on the skin area chosen for treatment and moveduniformly within it.

0.1-0.5 sec after detecting contact with the skin, the parameters offree oscillations are began to be measured, presenting the doctor theresults of measurement or the calculated values of the criterion.

When direct measurements are used (without averaging), the eliminationof redundant information is more important than during the sequentialmanner of treatment, that is why only the moments of achievement of thenew extremes are indicated (in one of the above mentioned ways).

During the averaging of results (with one or another method), either allthe results may be presented, or only the moments of achievement of thenew extremes.

Since there is no link between the sequential index of the electrodeplacing point and the treatment area in this case, recording the data bydevice is ineffective and the doctor should remember the place ofachievement of the new extreme.

All other ways of automating a sequential method of treatment (videorecording or recording data and locations of the electrodes by acomputer) are applicable to labile method.

According to the results of the optimal zone identification, aftersearching through the entire chosen skin area, the main therapy iscarried out, according to the chosen technique.

If several non-contiguous zones are found then the treatment of thesmallest zone is conducted.

The use of separated electrodes in both variants of a method is similarto the aforementioned, with the only difference that one of them isplaced outside the treatment zone, whereas the search is carried outwith the second electrode.

INDUSTRIAL APPLICABILITY

The group of inventions may be used in the treatment of variousdiseases, first of all, pain syndromes, regardless of their etiology, bystimulators which use inductive energy storage unit to generate stimuliand reduce the time of the procedures, improving the effectiveness ofthe treatment at the same time.

What is claimed is: 1.-6. (canceled)
 7. A method for adaptive electricstimulation of a living body that includes applying electrodes on abiological object's tissues and transmitting through them bursts ofelectrical stimuli generated using an inductive energy storage unit madeas an inductance coil or a transformer or an autotransformer,controlling an exposure duration and stimuli parameters based onparameters of free oscillations, arising in an oscillation circuitformed by an inductance of the storage unit and an impedance ofinterelectrode tissues, wherein the free oscillation parameters aremeasured while a current stimulus burst is acting and based on resultsof these measurements, one is controlling parameters of the stimuli inthe same burst or in any subsequent stimulus bursts, as well ascontrolling an onset of a next stimulus in the burst depending on aphase of the free oscillation of a previous stimulus.
 8. The method ofclaim 7, wherein the controlled stimulus parameter is a number ofstimuli in the burst.
 9. The method of claim 7, wherein the controlledstimulus parameter is a time interval between adjacent stimuli in theburst.
 10. The method of claim 7, wherein the controlled stimulusparameter is a waveform, include an amplitude and polarity, of eachstimulus in the burst.
 11. The method of claim 7, wherein the controlledstimulus parameter is a repetition rate of subsequent stimulus bursts.12. The method of claim 7, wherein the controlled stimulus parameter isan exposure duration.
 13. A method for adaptive electric stimulation ofa living body that includes applying electrodes on a biological object'stissues and transmitting through them bursts of electrical stimuligenerated using an inductive energy storage unit made as an inductancecoil or a transformer or an autotransformer, controlling an exposureduration and stimuli parameters based on parameters of freeoscillations, arising in an oscillation circuit formed by an inductanceof the storage unit and an impedance of interelectrode tissues, whereinone is measuring the free oscillation parameters of the last stimulus ina burst, and based on results of these measurements, one is controllingparameters of stimuli in any subsequent stimulus bursts, as well as iscontrolling an onset of a next stimulus in the burst depending on aphase of the free oscillation of a previous stimulus.
 14. The method ofclaim 13, wherein the controlled stimulus parameter is a number ofstimuli in the burst.
 15. The method of claim 13, wherein the controlledstimulus parameter is a time interval between adjacent stimuli in theburst.
 16. The method of claim 13, wherein the controlled stimulusparameter is a waveform, include an amplitude and polarity, of eachstimulus in the burst.
 17. The method of claim 13, wherein thecontrolled stimulus parameter is a repetition rate of subsequentstimulus bursts.
 18. The method of claim 13, wherein the controlledstimulus parameter is an exposure duration.
 19. A method for adaptiveelectric stimulation of a living body that includes applying electrodeson a biological object's tissues and transmitting through them bursts ofelectrical stimuli generated using an inductive energy storage unit madeas an inductance coil or a transformer or autotransformer, controllingan exposure duration and stimuli parameters based on parameters of freeoscillations, arising in an oscillation circuit formed by an inductanceof the said storage unit and an impedance of interelectrode tissues,wherein at an end of a burst and before a beginning of a next burst, aprobing stimulus is generated, wherein one is measuring parameters offree oscillations of the probing stimulus and, based on thesemeasurements, one is controlling stimulus parameters in any subsequentstimulus bursts, as well as is controlling an onset of a next stimulusin the burst depending on a phase of the free oscillation of a previousstimulus.
 20. The method of claim 19, wherein the controlled stimulusparameter is a number of stimuli in the burst.
 21. The method of claim19, wherein the controlled stimulus parameter is a time interval betweenadjacent stimuli in the burst.
 22. The method of claim 19, wherein thecontrolled stimulus parameter is a waveform, include an amplitude andpolarity, of each stimulus in the burst.
 23. The method of claim 19,wherein the controlled stimulus parameter is a repetition rate ofsubsequent stimulus bursts.
 24. The method of claim 19, wherein thecontrolled stimulus parameter is an exposure duration.